Abstract: A chemical filter unit 10 is made of a chemical filter 12 and a filter life detection sensor 1. The filter life detection sensor 1 is provided with an adsorption state detection sensor 3 and a reference sensor 4 to which a flow of air is blocked. The sensors 3 and 4 are made of the same filter material as the chemical filter 12 with a pair of electrodes sandwiching the filter material. An oscillation circuit, in which the sensors 3 and 4 constitute a part of the oscillating conditions, detects changes in impedance of the sensors 3 and 4 based on the changes in oscillation frequencies. A measurement of the adsorption state detection sensor 3 is corrected with a measurement of the reference sensor 4 in order to remove effects of temperature and humidity, obtain a measurement corresponding to the amount of adsorption of chemical substances, and decide on the timing of replacing the chemical filter based on the corrected measurement.

Abstract: A chemical filter unit 10 is made of a chemical filter 12 and a filter life detection sensor 1. The filter life detection sensor 1 is provided with an adsorption state detection sensor 3 and a reference sensor 4 to which a flow of air is blocked. The sensors 3 and 4 are made of the same filter material as the chemical filter 12 with a pair of electrodes sandwiching the filter material. An oscillation circuit, in which the sensors 3 and 4 constitute a part of the oscillating conditions, detects changes in impedance of the sensors 3 and 4 based on the changes in oscillation frequencies. A measurement of the adsorption state detection sensor 3 is corrected with a measurement of the reference sensor 4 in order to remove effects of temperature and humidity, obtain a measurement corresponding to the amount of adsorption of chemical substances, and decide on the timing of replacing the chemical filter based on the corrected measurement.

Abstract: A first device (1) and a second device (2) can be communicated by an electromagnetic coupling. Data to be transmitted from the first device to the second device is converted into pulse signals of different duty ratios in accordance with the H or L level of the transmission data. Further, the oscillation of an oscillator (15) of the first device is intermittently performed in accordance with the H/L level of the pulse signal. Switching elements (39, 40) are provided for a resonance circuit (30) provided in the second device. When data is transmitted from the second device to the first device, the switching elements are turned on or off in accordance with the data. Thus, the electromagnetic coupling is intermittently performed. The oscillator of the first device at that time intermittently executes the oscillation at a third duty ratio.